Presence of bridge piers across a stream causes constricted flow in the openings due to the decrease of width of stream owing to presence of the piers. Furthermore it creates the following problems from hydraulic point of view: 

(i)  Local scouring at the piers and bed erosion can take place. To avoid damage to the foundation of piers, a number of protective layers of stone or concrete apron could be provided around the piers.

(ii) The head loss induced by bridge piers causes the backwater effect so that water level upstream is increased. Thus this may result in flooding in upstream areas.